[Mristudio-users] Adjusting Gradients for Oblique Angles
Hangyi Jiang
hjiang at jhmi.edu
Fri Dec 10 09:07:18 EST 2010
hello,
the 3rd row should be the outer product of the given two vectors, not [0,0,1]
regards
hangyi
________________________________
From: mristudio-users-bounces at mristudio.org [mristudio-users-bounces at mristudio.org] On Behalf Of Rajagopalan, Venkateswaran [rajagov2 at ccf.org]
Sent: Friday, December 10, 2010 9:01 AM
To: DTI Studio, ROI Editor, DiffeoMap Questions/Support
Subject: Re: [Mristudio-users] Adjusting Gradients for Oblique Angles
Dear Jeff Sadino,
This is what I did for manual oblique angle correction
multiply your gradient matrix (I don't know how many directions you have) if you have 12 directional data then you will have 3*13 (one b=0 values too) with the "Image Orientation patient" matrix
[ 1 0 0 0 .8846 -.4664] rewritten as (these are unit vectors with z direction being 0 0 1 not mentioned in the Image Image orientation patient from Dicom header
[ 1 0 0
0 0.8846 -0.4664
0 0 1]
3*3
Multiply the ablove Image orientation patient with your gradient matrix.
Thanks
Venkat
________________________________
From: mristudio-users-bounces at mristudio.org on behalf of Jeff Sadino
Sent: Thu 12/9/2010 6:09 PM
To: DTI Studio, ROI Editor, DiffeoMap Questions/Support
Subject: [Mristudio-users] Adjusting Gradients for Oblique Angles
Hello,
Thank you for the DTI training session in Turtle Bay last week. It was very helpful for us!
I am wondering how to manually adjust the gradients for an oblique angle. I am using Siemens 3T Trio Tim VB17.
My default gradient (for one direction) is:
0.861, -0.366, 0.354
After clicking "Rotate gradients if applicable" in DTIStudio 3.0.2 (March2010), the gradient is:
0.861, -0.489, 0.142
I couldn't find exactly which tag in the DICOM header contains the rotation information. The closest I could find is "ImageOrientationPatient". The value for this is:
[ 1 0 0 0 .8846 -.4664]
How do I go from the default gradient to the rotated gradient? Also, can I use this same method on the VB13 and VA25 software?
Thank you very much for your help!
Jeff Sadino
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